The invention relates to a lock for safety belts, having a lock housing and an inner housing positioned within the lock housing and held in place by spring tension. A latch tongue is insertable into the inner housing and a latch is located within the inner housing, and is adapted to seat in a depression in the latch tongue, with the latch tongue inserted into the inner housing, and held there by spring tension, so as to prevent the withdrawal of the latch tongue from the inner housing. The lock housing is also provided with an externally operable key, journalled in the lock housing.
The lock has the function in seatbelts, as used to secure passengers in aircraft and surface vehicles, to reliably maintain the seatbelt in the buckled state under all conditions of loading, and to permit an easy opening of the seatbelt, when required to do so.
In seatbelt locks of the prior art, a spring-loaded latch, movably located within the lock housing, seats in a depression in the latch tongue. The release of the lock is accomplished through a key, slideably or pivotably located within the lock housing, which, upon actuation through pressure, lifts the latch out of the depression in the latch tongue against its spring loading, so that the latch tongue is released.
In the seatbelt lock defined in the introductory paragraph, as described in German Published Patent Application No. 2 345 593, the latch tongue is not inserted into the lock housing itself but into an inner housing, held reciprocably in the lock housing by means of strong tension springs. This capacity for lateral displacement is utilized in the known belt lock to arm an automatic release mechanism which opens the belt lock automatically, upon the lapse of a pre-determined time delay. The inner housing is displaced, with respect to the lock housing, under the influence of the strong tensile forces induced by the collision in an accident, and the release mechanism is armed. Should the tensile loading relax after the impact, the lock mechanism opens automatically--after a time delay of a few seconds, for reasons of safety--so that the belted person can free himself of the belt without difficulties, or may be released by others, even if unfamiliar with the belt mechanism, from the safety belt.
It is necessary, so that the safety belt may fulfill its function properly, that the opening of the lock may be accomplished with a small pressure load, imposed upon the release key. Only in such circumstances can the belt be opened without diffculty by a person injured in an accident, or by a fellow passenger. According to the latest guidelines, the pressure load required for opening should not exceed a maximum value of 6,000 grams.
This requirement can be met without difficulty, through the appropriate choice of the spring loading exerted on the latch, as long as the lock is not subjected to any tensile load.
In the event of an accident, however, strong tensile loads may be exerted on the lock. This may occur because the belted person may hang in the belt with his body weight, e.g. through being unconscious, or through the vehicle being upended as a consequence of the accident.
Even the automatic release mechanism, described in German Published Patent Application No. 2 345 593, only releases the belt lock when the tensile loading is removed. It is ensured therethrough, that an unconscious person--in a vehicle lying on its roof after the accident, for example--is retained in the safety belt until his body is lifted by helpers and the belt becomes unloaded. This has the consequence, however, in the event of a maintained tensile loading of the belt lock, such as may be occasioned by the deformation of the vehicle body or of the seat structure, in the accident, the automatic release mechanism does not come into play.
The latch is clamped into the depression of the latch tongue by these tensile loads imposed on the belt lock, so that a substantially larger pressure load must be developed on the release key to lift the latch out of the depression. It has been possible in the past, through suitable shaping of the latch and of the mating depression, to maintain the upper limit of 6,000 grams for the pressure load, as long as the tensile load on the belt lock does not exceed 30,000 grams. With higher tensile loads, the pressure load required to release locks of the prior art rises rapidly to values of 15,000 to 20,000 grams. Such loads can hardly be developed under favorable circumstances. Under the unfavorable circumstances of an accident the locks of the prior art cannot, for all practical consequences, be manually opened at tensile loadings exceeding 30,000 grams.